1. Field of the Invention
The present invention relates to a wireless communication apparatus and a method for a multiple transmit and receive antenna system using multiple codes, and more particularly to an apparatus and a method, which can allocate transmit power depending on transmit signals.
2. Description of the Related Art
Generally, a Bell Labs layered space-time (BLAST) system uses a multiple transmit-receive antenna. The BLAST system employs suitable signal processing at a receive end to improve spectral efficiency. In other words, a high data rate is achieved by transferring independent substreams from multiple transmit/receive antennas under a rich-scattering wireless channel environment employing channels independent of each other between transmit/receive antennas. Each transmitted signal from each transmit antenna is detected in a predetermined order according to channel conditions, and an already-detected transmitted signal is treated through a Successive Interference Cancellation (SIC) process in which a corresponding component is subtracted from a received signal when detecting the next transmitted signal. Herein, from among BLAST systems, a scheme to greater simplify signal processing by independently coding substreams is a Vertical BLAST (V-BLAST).
Meanwhile, a multi-code CDMA system has been suggested as a transmission scheme for a high and variable data rate. Herein, according to a primary notion of the multi-code CDMA system, data of a certain user are divided into several streams and transferred in parallel by allocating an orthogonal code to each stream. Accordingly, the V-BLAST system employing the multi-code CDMA transmission scheme is expected to be an important telecommunication system in a next generation mobile telecommunication, which will require a high data rate.
A reception scheme of and a performance analysis about the V-BLAST system performed until now have been deployed under a frequency-flat fading channel environment, that is, based on the assumption that a propagation delay duration is much smaller than a symbol duration. However, signals are seriously distorted under the frequency-flat fading channel environment having a propagation delay. This phenomenon is a more serious problem under a high-speed data telecommunication environment in which the symbol duration is very short. Therefore, under the frequency-selective fading channel environment, although the multi-code V-BLAST system employs orthogonal codes, an interference occurrence between codes is inevitable. Accordingly, it is necessary to remove the interference occurrence between codes.
A conventional method employs a group detection technique used in a CDMA system in order to remove correlation between codes. However, a maximum dimension of a matrix required while inverting a matrix for a group decorrelating detector through the group detection technique is equal to a number obtained after multiplying the number of antennas by the number of codes. Accordingly, as the number of used codes increases, a computation amount remarkably increases, and the group detection technique will encounter serious problems when applied to a real system.
Conventional techniques also include a technique for removing Multi-Code Interference (MCI) by using a parallel interference cancellation scheme in a multi-code system of a single transmit-receive antenna. However, since the technique has to simultaneously process received signals de-spread with respect to all codes, the technique has a problem in that hardware complexity increases in proportion to the number of codes. On the other hand, since a SIC scheme individually processes each received signal for each code in order, the SIC scheme has a relatively low hardware complexity as compared with a Parallel Interference Cancellation (PIC) scheme.
Meanwhile, according to a characteristic of a multi-code system, all transmitted signals corresponding to each code reach a receive end through the same channel. Herein, after de-spreading the transmitted signals, a receive power difference can exist due to difference between correlation values of codes. However, in the multi-code system, intensity of receive power seldom exists with respect to all codes. This is a characteristic different from an uplink multi-user CDMA environment. Generally, in the SIC scheme, a signal with the greatest strength is detected first of all, so that reliability increases. Accordingly, if the SIC scheme is employed to mitigate MCI, a process for detection ordering employed through a conventional SIC scheme will have a negligible effect. Accordingly, it is necessary to overcome performance limitations for successive MCI cancellation methods caused by the SIC scheme.